A girl picks panda souvenirs at Berlin Zoo in Berlin, Germany, June 9, 2018. Mengmeng and Jiaoqing, the two giant pandas from China, arrived in Berlin on June 24, 2017. They became superstar during their first-year's stay here in Berlin Zoo. (Xinhua/Shan Yuqi)

A guest takes photos of giant panda Jiaoqing at Berlin Zoo in Berlin, Germany, June 9, 2018. Mengmeng and Jiaoqing, the two pandas from China, arrived in Berlin on June 24, 2017. They became superstar during their first-year's stay here in Berlin Zoo. (Xinhua/Shan Yuqi)

Guests visit giant panda Jiaoqing at Berlin Zoo in Berlin, Germany, June 9, 2018. Mengmeng and Jiaoqing, the two pandas from China, arrived in Berlin on June 24, 2017. They became superstar during their first-year's stay here in Berlin Zoo. (Xinhua/Shan Yuqi)

Panda souvenirs are seen at Berlin Zoo in Berlin, Germany, June 9, 2018. Mengmeng and Jiaoqing, the two pandas from China, arrived in Berlin on June 24, 2017. They became superstar during their first-year's stay here in Berlin Zoo. (Xinhua/Shan Yuqi)

Panda souvenirs are seen at Berlin Zoo in Berlin, Germany, June 9, 2018. Mengmeng and Jiaoqing, the two pandas from China, arrived in Berlin on June 24, 2017. They became superstar during their first-year's stay here in Berlin Zoo. (Xinhua/Shan Yuqi)

A guest visits giant panda Mengmeng at Berlin Zoo in Berlin, Germany, June 9, 2018. Mengmeng and Jiaoqing, the two pandas from China, arrived in Berlin on June 24, 2017. They became superstar during their first-year's stay here in Berlin Zoo. (Xinhua/Shan Yuqi)